Transmission control apparatus for an automatic transmission

ABSTRACT

The improved CVT control apparatus for a vehicle is disclosed. By using the CVT control apparatus, it becomes possible that the drive feeling is constant independently of a running state, the vehicle is accelerated as the driver&#39;s intention if accelerated due to the actuation of an accelerator pedal, and the run of the vehicle is performed so as to improve the fuel consumption rate if the acceleration is not required.  
     By always calculating a correct driving torque, the transmission gear ratio is calculated to obtain the target driving torque set based on the amount of actuation of an accelerator pedal, and the obtained target driving torque is corrected by the gradient of a road obtained from the calculated driving torque. Further, the gear ratio which aims at the improvement of acceleration and the gear ratio which aims at the improvement of the rate of fuel consumption are weighted and combined with each other, and the optimum gear ratio is obtained by using fuzzy inference.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a transmission control apparatusfor an automatic transmission of a vehicle, and more particularly to acontrol apparatus for a continuously variable transmission (CVT)suitable for a vehicle which can accelerate comfortably based on thedriver's intention or the running state of the vehicle and can run withtaking the fuel consumption into consideration when the acceleration isnot required and a control method thereof.

[0002] In a vehicle with the continuously variable transmission, thespeed is generally changed by using a control map in which values of thetransmission gear ratio pre-determined by the vehicle speed and thethrottle opening are represented as a table.

[0003] However, in such a control method, it is required topre-determine a control constant in consideration of various drivingconditions when the design or the development of the vehicle is made. Itis a task called as tuning or matching, which takes a lot of doing andthus time.

[0004] To solve such a problem, it is thought to eliminate the timerequired to tune by using a control method in which the optimumtransmission gear ratio is calculated during run of the vehicle. Forexample, the method proposed by us is disclosed in Japanese PatentApplication Laid-Open No. 7-174219 (1995). However, in this method, theactual driving torque follows the predetermined target value or thetarget driving torque. There is, therefore, a problem that even thoughnew target driving torque revised according to the situation ispreferable, it is impossible to control the transmission gear ratio bysetting the new target driving torque as a target value.

SUMMARY OF THE INVENTION

[0005] An object of the present invention is to provide an improved CVTcontrol apparatus for a vehicle, in which the time required to tune canbe remarkably decreased. By using the improved CVT control apparatus, itbecomes possible that the drive feeling is constant independently of therunning state, the vehicle is accelerated as the driver's intention ifaccelerated due to the actuation of an accelerator pedal, and the run ofthe vehicle is performed so as to improve the fuel consumption rate ifthe acceleration is not required.

[0006] Therefore, by calculating the correct driving torque every timein the present invention, the transmission gear ratio is calculated toobtain the target driving torque set based on the amount of actuation ofan accelerator pedal, and the obtained target driving torque iscorrected by the gradient of a road obtained from the calculated drivingtorque. Further, the gear ratio which aims at the improvement ofacceleration and the gear ratio which aims at the improvement of therate of fuel consumption are weighted and combined with each other, andthe optimum gear ratio is obtained by using fuzzy inference.

[0007] Because the target driving torque is set according to a state atthat time during run of a vehicle, and the transmission gear ratio isdetermined by using the target driving torque, the drive feeling is notchanged even if the circumstance of run is changed. Further, the vehiclecan be accelerated as the driver's intention at the time of theacceleration due to the actuation of the accelerator pedal, and run ofthe vehicle is performed so as to improve the fuel consumption rate ifthe acceleration is not required.

[0008] Other objects and features of the present invention will be moreapparent to those skilled in the art on consideration of theaccompanying drawings and following specification wherein are disclosedseveral exemplary embodiments of the invention with the understandingthat such variations, modifications and elimination of parts may be madetherein as fall within the scope of the appended claims withoutdeparting from the spirit of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a view showing the whole configuration of a controlsystem of the vehicle installing a continuously variable transmission(CVT) to which the present invention is applied.

[0010]FIG. 2 is a block diagram showing the hardware configuration of acontrol apparatus using a microcomputer.

[0011]FIG. 3 is a block diagram showing the configuration of a controlapparatus according to a first embodiment of the present invention.

[0012]FIG. 4 is a block diagram showing the configuration of an outputtorque calculating means shown in FIG. 3.

[0013]FIG. 5 is a block diagram showing the configuration of a controlapparatus according to a second embodiment of the present invention.

[0014]FIG. 6 is a block diagram showing the configuration of a roadgradient estimating and calculating means.

[0015]FIG. 7 is a block diagram showing the configuration of a controlapparatus according to a third embodiment of the present invention.

[0016]FIG. 8 is a block diagram showing the configuration of a means forcalculating the gear ratio which provides the optimum fuel consumptionrate shown in FIG. 7.

[0017]FIG. 9 is a flow chart illustrating the operation of a minimumfuel-consumption-rate determining unit in the means for calculating thegear ratio which provides the optimum fuel consumption rate shown inFIG. 8.

[0018]FIG. 10 is a fuzzy rule table used for fuzzy inference, whichcomposes a weighting and combining means shown in FIG. 7.

DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0019] An embodiment of the present invention will be explainedhereinafter with reference to drawings.

[0020]FIG. 1 is a view showing the driving system of the vehicleinstalling a control system for a continuously variable transmission(CVT) to which the present invention is applied.

[0021] Wheels 103 are driven by an output given from an engine 101through a CVT 102. In the present embodiment, the CVT 102 is a belt typeone. The width of a groove of a pulley is changed by a oil pressure.While the belt type CVT is used in this embodiment, another type CVTsuch as a toroidal type one may be used in the same way. The CVT 102comprises a torque converter 104, a back and forth travel gear 105, atransmission mechanism 106 having a pulley of which groove width isvariable and a belt, and a row of transmitting gear 107 including adifferential gear, these mechanism are controlled a control apparatus108.

[0022] The control apparatus 108 has the hardware configuration shown inFIG. 2, including a microcomputer. A microprocessor 201 of themicrocomputer 108 reads programs or data from a read only memory (ROM)202, and performs an numerical operation or a logical operation by usinga random access memory (RAM). Further, the microprocessor 201 inputsinput signals from various kind of sensors 204, 205 through inputcircuits 206, 207, performs an arithmetic operation, and operatesactuators 210, 211 through output circuits 208, 209.

[0023] A software for the control apparatus 108 shown in FIG. 1comprises an engine control logic 109 for controlling the engine 101 anda CVT control logic 110 for controlling the CVT 102. The engine controllogic 109 inputs an intake air amount signal a obtained by measuring theair amount passing through an air filter 111 by an air flow meter 112, athrottle opening signal b corresponding to an operated angle of athrottle valve 114 actuated by an accelerator pedal 113, a crank anglesignal c or an output of a crank angle sensor 115, and a signal gindicative of the amount of oxygen remained in an exhaust gas, which isobtained from an O₂ sensor 116, as input signals from the engine 101.The engine control logic 109 outputs, for example, a fuel injectionsignal d for providing the pulse width corresponding to the fuel amountto an injector 117, an ignition signal e for controlling the operationtiming of an ignition plug 118, and an EGR signal f for controlling acirculating gas valve (not shown), as output signals.

[0024] The CVT control logic 110 inputs an input engine speed signal iobtained by a rotation sensor 119 provided against a primary pulley ofthe CVT 102, operation oil temperature signal l of an oil pressurecircuit 120, and an output engine speed signal m obtained by a rotationsensor 121 provided against a secondary pulley. Further, the CVT controllogic 110 outputs a lock-up control signal h for connecting directly theinput/output of the torque converter, a line pressure control signal jfor controlling the whole oil pressure, and a speed-change controlsignal k for controlling a transmission speed ratio of the transmissionmechanism 106.

[0025] While the engine and the transmission are controlled by onecontrol apparatus in the example of FIG. 1, it is needless to say thatthose can be controlled by different control apparatus.

[0026]FIG. 3 shows a first embodiment of the configuration of the gearratio control logic used in the present invention, and represents thecontent of a CVT control logic 110 of FIG. 1. When the accelerator pedal113 is stepped down, the throttle sensor 114 provided in the throttlevalve is actuated and a throttle opening TVO included in the throttleopening signal b is changed. A target torque generating means 301retrieves the torque which produces the acceleration in which thepassenger comfort is provided at the vehicle speed corresponding to theoutput speed (rotational number) No included in an output speed signal mand the throttle opening TVO, and outputs the torque as a target outputtorque tTo. Namely, as the magnitude of actuation of the acceleratorpedal is large, the target output torque is increased. Even if themagnitude of the actuation is the same, the target torque generatingmeans 301 can generate the target output torque tTo by which comfortableacceleration in human technology is obtained, by setting larger targettorque so as to obtain larger acceleration at low speeds and by settingsmaller target torque at high speeds.

[0027] While, an output torque calculating means 302 calculates outputtorque To by using an engine speed Ne obtained from the crank anglesignal c and a throttle opening TVO and a turbine speed Nt obtained fromthe input speed (rotational number) signal i, as described later.Further, a gear ratio control means 304 compares the target outputtorque tTo with output torque To, generates a gear-ratio-variationsignal Δ R by adjusting gain of the obtained difference by a controlcorrecting unit, adds it to the current gear ratio R calculated by agear ratio calculating block 305, and controls the transmission gearratio of the CVT 2. Namely, in order to bring the output torque To closeto the target output torque tTo, the gear ratio is decreased if theoutput torque is larger, and the gear ratio is increased if smaller. Thevariation continues until the output torque almost becomes equal to thetarget. This means forms a feedback control loop.

[0028]FIG. 4 shows in more detail the configuration of an output torquecalculating means 302 shown in FIG. 3. A block 401 calculates the speedratio e of the torque converter at divider unit 405, by using the enginespeed Ne obtained from the crank angle sensor 115 and the turbine speedNt obtained from the rotation sensor 119. By inserting the speed ratio einto an input capacitance coefficient characteristic 406 of the torqueconverter, an input capacitance coefficient Cp is obtained. Further, bymultiplying Cp by the square of the engine speed Ne at a multiplier unit407, the input torque of the converter or the pump torque Tp isobtained.

[0029] In FIG. 4, the pump torque is calculated also by using anotherway. The two pump torque are switched according to the state. Therefore,the calculation of torque is carried out with high accuracy. Namely, ablock 402 including an engine torque map 413 retrieves the engine torqueTe based on the throttle opening TVO and the engine speed Ne, adds thecorrection of the components of inertia of blocks 414, 415, andcalculates the pump torque Tp. Either an output of the block 401 or thatof the block 402 is selected based on the speed ratio e by a change-overdetermining logic 411.

[0030] While, because the torque ratio t is obtained by providing thespeed ratio e to the torque ratio characteristics 408 of the torqueconverter, the output torque of the torque converter or the turbinetorque Tt is obtained by multiplying the torque ratio t by the selectedpump torque Tp by the multiplier unit 409. Further, because the gearratio R of a pulley can be calculated by obtaining the ratio of theoutput speed No obtained from the rotation sensor 121 and turbine speedNt by the divider unit 411, the output torque To is calculated bymultiplying the gear ratio R by the turbine torque Tt by multiplier unit412.

[0031] Because the output torque follows the target driving torque setsuitably by the operation of the feedback control loop according to thepresent invention, it is possible to obtain the comfortable feeling ofacceleration corresponding to the actuation angle of an acceleratorpedal. Further, because the comfortable feeling of acceleration isdetermined in the human technology, regardless of the kind of vehicles,it is not necessary to perform the task of the matching of thecharacteristics of driving forces every kind of vehicles, i.e. thetuning task, and thus it becomes possible to decrease remarkably thenumber of steps of development.

[0032] Because the output torque is obtained by the output torquecalculating means 302 in the present invention, it is not required toprovide with a high expensive torque sensor. It is not to say that thesame control is realized by providing the torque sensor on an outputshaft.

[0033] It should be noted that the CVT 102 is not limited to a generaltransmission mechanism utilizing an oil pressure. It may use anothertransmission mechanism in which the gear ratio is changed by changingthe width of grooves of a pulley by a electric motor. Further, it mayuse not only a belt type transmission mechanism, but also a toroidaltype one in which a friction wheel is used.

[0034]FIG. 5 shows the configuration of a gear ratio control logicaccording to a second embodiment of the present invention. The samereference number as FIG. 3 designates like components. The differencesbetween FIGS. 3 and 5 are in that a road gradient estimating andcalculating means 502 is provided and thus the configuration of thetarget output torque generating means 501 is somewhat different.

[0035] The target output torque generating means 501 retrieves torquewhich produces the acceleration by which a driver feels comfortable at acurrent vehicle speed, and outputs it as a target output torque tTo.However, because the acceleration by which the driver can feelcomfortable is different between in a slope and in a flat road, athree-dimensional look-up map is used and the target output torquepattern is changed based on a gradient signal.

[0036]FIG. 6 shows an algorithm for obtaining the gradient signal in theroad gradient estimating and calculating means 502 of FIG. 5. The outputtorque To calculated in the output torque calculating means 302 is inputto a final stage gear unit 601 in which the output torque To ismultiplied by a final stage gear ratio Gf and the torque Td of a drivingshaft is obtained. While, because a vehicle running resistance TR1 ischanged due to the vehicle speed, the vehicle running resistancesuitable for the vehicle is pre-stored in a map 602 for the vehiclerunning resistance. The vehicle running resistance TR1 is retrieved byusing a vehicle speed Vsp obtained by multiplying the output speed No bya conversion coefficient at a unit 603. At a unit 604, the accelerationis obtained by the differentiation of the vehicle speed Vsp. Theacceleration is multiplied by vehicle weight M at a unit 605, and thenmultiplied by a radius r of a tire at a unit 606. As a result,acceleration resistance torque Ta is provided as an output of the unit606. By subtracting these resistance torque TR1 and Ta from the obtainedoutput torque To, the gradient resistance torque Tgr is obtained. Agradient Grd can be obtained by multiplying the torque Tgr by theconversion coefficient.

[0037] Because in the method of the present invention the driving torquecorresponding to the variation of the feeling of acceleration isobtained even if the gradient of a road is changed, the comfortablefeeling of acceleration is always obtained even in a slope. Further,because the road gradient is calculated during run of the vehicle, theabove function is realized without using a high expensive slope sensoror acceleration sensor.

[0038]FIG. 7 shows the configuration of a gear ratio control logicaccording to a third embodiment of the present invention. There isprovided means 701 for calculating the gear ratio which provides theoptimum fuel consumption rate, means 702 for recognizing driver'sintention and environment and weighting and combining means 703 in theconfiguration shown in FIG. 7, different from the configuration of FIG.5.

[0039] The means 701 for calculating the gear ratio which provides theoptimum fuel consumption rate includes a characteristic map indicativeof the amount of fuel consumption of an engine. The means 701 calculatesthe current amount of fuel consumption by using a throttle opening TVO,an output speed No, an engine speed Ne, a turbine speed Nt, and outputtorque To calculated by the output torque calculating means 302,calculates the amount of fuel consumption under the assumption that thegear ratio is changed by a little, determines the direction of the gearratio in which the fuel consumption rate is improved, and generates afirst gear-ratio-variation signal Δ R1.

[0040] Further, the output torque To is compared with the target outputtorque tTo as in the case of the embodiment of FIG. 2, and the obtaineddifference is set as a second gear-ratio-variation signal Δ R2.

[0041] These signals Δ R1 and Δ R2 are input to the weighting andcombining means 703. In the means 703, the rate of the weighting isdetermined according to an output Dw of the means 702 for recognizingdriver's intention and environment and then combined.

[0042] An output of the weighting and combining means 703 is adjusted inits gain by the control correcting unit 303, and a thirdgear-ratio-variation signal Δ R3 is generated. The signal Δ R3 is addedto the current gear ratio R calculated by the gear ratio calculatingblock 305. The gear ratio of the CVT 2 is controlled by the addedsignal.

[0043] If the driver's intention Dw aims at the improvement ofacceleration performance, the output of the weighting and combiningmeans 703 approaches to the second gear-ratio-variation signal Δ R2. Asa result, the gear ratio is controlled so as to produce the torque bywhich the comfortable acceleration is obtained. On the contrary, if thedriver does not almost move the accelerator pedal, the means 702 forrecognizing the driver's intention and environment recognizes norequirement of acceleration. As a result, the output of the weightingand combining means 703 approaches to the first gear-ratio-variationsignal Δ R1 and the gear ratio is changed so that amount of fuelconsumption may be lessened. Generally, the weighting is performedbetween R1 and R2, and thus the gear ratio is controlled according tothe output Dw of the means 702 for recognizing the driver's intentionand environment with keeping the balance of the feeling of accelerationand the fuel consumption rate.

[0044]FIG. 8 shows the configuration of means 701 for calculating thegear ratio which provides the optimum fuel consumption rate shown inFIG. 7.

[0045] In FIG. 8, the engine torque Te can be retrieved by providing thethrottle opening TVO and the engine speed Ne to an engine torquecharacteristic map 801. Further, by providing the obtained engine torqueTe and the engine speed Ne to a fuel consumption amount characteristicmap 802, the amount Qf of fuel consumption is obtained. The current gearratio R can be obtained from the output speed No and the turbine speedNt. The results obtained by adding and subtracting the predeterminedvariation component Δ R of the gear ratio, respectively, to and from thegear ratio R, are input to a torque converter speed correcting unit 803.The result (R−Δ R) obtained by subtracting the variation component ofthe gear ratio is multiplied by the output speed No. As a result, thetemporal turbine speed Nt′ is obtained and then the square of Nt′ iscalculated.

[0046] While, the temporal turbine torque Tt′ is calculated from theoutput torque To and (R−ΔR), and then the temporal capacitancecoefficient Cp′ is obtained from Tt′ and the square of the turbinespeed. Further, the temporal speed ratio e′ is calculated by retrievingthe capacitance coefficient characteristic map 804, and the temporalengine speed Ne′ is obtained by dividing the temporal turbine speed Nt′by the temporal speed ratio e′. Therefore, the temporal fuel consumptionamount Qf′ can be obtained in the same way as mentioned above.

[0047] Also if the temporal turbine torque Tt′ is calculated from theoutput torque To and (R+ΔR), the temporal fuel consumption amount Qf″can be obtained just in the same way as mentioned above.

[0048] Both Qf′ and Qf″ are compared with the current fuel consumptionamount Qf by the minimum fuel consumption rate determining unit 805.Next, the direction of the variation of the gear ratio in which the fuelconsumption rate is improved is determined, and the firstgear-ratio-variation signal Δ R1 is output.

[0049]FIG. 9 is a flow chart illustrating the logic of a minimumfuel-consumption-rate determining unit 805 of FIG. 8.

[0050] In FIG. 9, three fuel consumption amounts Qf, Qf′, Qf″ are readat step 1, and Qf is compared with Qf′ at step 2. If Qf′ is smaller thanQf, then because the fuel consumption rate is improved as the gear ratiobecomes smaller, the processing advances to step 3, in which thegear-ratio-variation component is set to (ΔR1=−ΔR).

[0051] If Qf′ is larger than Qf, then Qf is compared with Qf″ at step 4.If Qf″ is smaller than Qf, then because the fuel consumption rate isimproved as the gear ratio becomes smaller, the processing advances tostep 5, in which the gear-ratio-variation component is set to (ΔR1=+ΔR).

[0052] If Qf″ is larger than Qf, then because both Qf′ and Qf″ arelarger than Qf, the processing advances to step 6, in which the gearratio is set to (ΔR1=0) or kept as it is.

[0053] The detail of the means 702 for recognizing the driver'sintention and environment is abbreviated here.

[0054] It is convenient to use the fuzzy inference in the weighting andcombining means 703. An example of the rule of the fuzzy inference isshown in FIG. 10. The rule of FIG. 10 is determined so that the thirdgear-ratio-variation signal Δ R3 may be output according to thecombination of respective states, by setting the firstgear-ratio-variation signal Δ R1 for obtaining the optimum fuelconsumption rate, the second gear-ratio-variation signal Δ R2corresponding to the torque difference and the driver's intention Dw foracceleration as input variables. A membership function is set by usingthis rule, and the weighting and combining processing is performed. Inpartially spaced parts in FIG. 10, the rule is abbreviated. Those partsare filled due to the function of interpolation of the fuzzy inference.

[0055] It is further understood by those skilled in the art that theforegoing description is a preferred embodiment of the disclosedapparatus and that various changes and modifications may be made in theinvention without departing from the spirit and scope thereof.

What is claimed is:
 1. A control apparatus for an automatic transmissionof a vehicle including a gear ratio calculating unit for controlling theautomatic transmission to transfer an output of an engine of the vehicleto driven wheels after changing the gear ratio, and calculating the gearratio, and a speed-change control unit for controlling the gear ratiobased on the result of the calculation, comprising: a target drivingtorque generating unit for generating a value of the target drivingtorque based on a adaptation coefficient indicative of a running stateand a vehicle speed, a driving torque calculating unit for calculating avalue of driving torque based on the adaptation coefficient, the vehiclespeed and the engine speed, a correcting unit for obtaining a correctingvalue for correcting the value of the target driving torque based on thevalue of the driving torque calculated by said driving torquecalculating unit and correcting the target driving torque, agear-ratio-change-command unit for generating agear-ratio-change-command based on the correction value obtained by saidcorrecting means and commanding the change in the gear ratio, whereinsaid speed-change control unit changes the gear ratio based on thegear-ratio-change-command from the gear-ratio-change-command unit.
 2. Acontrol apparatus for an automatic transmission of a vehicle accordingto claim 1 , wherein the value of the target driving torque isdetermined due to the characteristics of the target driving torquepredetermined based on the adaptation coefficient and the vehicle speed.3. A control apparatus for an automatic transmission of a vehicleaccording to claim 1 , wherein the adaptation coefficient is throttleopening of a throttle valve for controlling the amount of air taken intothe engine of the vehicle.
 4. A control apparatus for an automatictransmission of a vehicle including a gear ratio calculating unit forcontrolling the automatic transmission to transfer an output of anengine of the vehicle to driven wheels after changing the gear ratio,and calculating the gear ratio, and a speed-change control unit forcontrolling the gear ratio based on the result of the calculation,comprising: a road gradient calculating unit for calculating gradient ofa road, a target driving torque generating portion for generating avalue of the target driving torque based on a adaptation coefficientindicative of a running state, a vehicle speed and the road gradient, adriving torque calculating unit for calculating a value of drivingtorque based on the adaptation coefficient, the vehicle speed and theengine speed, a correcting means for obtaining a correcting value forcorrecting the value of the target driving torque based on the value ofthe driving torque calculated by said driving torque calculating unitand correcting the target driving torque, a gear-ratio-change-commandmeans for generating a gear-ratio-change-command based on the correctingvalue obtained by said correcting means and commanding the change in thegear ratio, wherein said speed-change control unit changes the gearratio based on the gear-ratio-change-command from thegear-ratio-change-command means.
 5. A control apparatus for an automatictransmission of a vehicle according to claim 4 , wherein the value ofthe target driving torque is determined due to the characteristics ofthe target driving torque predetermined based on the adaptationcoefficient, the vehicle speed and the road gradient.
 6. A controlapparatus for an automatic transmission of a vehicle according to claim4 , wherein the road gradient is calculated based on the vehicle speedand the value of the driving torque calculated by the driving torquecalculating unit.
 7. A control apparatus for an automatic transmissionof a vehicle including a gear ratio calculating unit for controlling theautomatic transmission to transfer an output of an engine of the vehicleto driven wheels after changing the gear ratio, and calculating the gearratio, and a speed-change control unit for controlling the gear ratiobased on the result of the calculation, comprising: a fuel consumptionamount calculating unit for calculating the amount of fuel consumption,a first gear-ratio-change-command unit for generating a firstgear-ratio-change-command, based on the value of the fuel consumptionamount calculated by the fuel consumption amount calculating unit, aroad gradient calculating unit for calculating gradient of a road, atarget driving torque generating portion for generating a value of thetarget driving torque based on a adaptation coefficient indicative of arunning state, a vehicle speed and the road gradient, a driving torquecalculating unit for calculating a value of driving torque based on theadaptation coefficient, the vehicle speed, the engine speed and aturbine speed, a second gear-ratio-change-command unit for correctingthe target driving torque based on the value of the driving torquecalculated by said driving torque calculating unit and generating asecond gear-ratio-change-command, a means for recognizing driver'sintention and running environment according to the adaptationcoefficient and the vehicle speed, a fuzzy inference means forgenerating a third gear-ratio-change-command based on an output value ofthe first gear-ratio-change-command means, an output value of the secondgear-ratio-change-command means, an output value of the means forrecognizing driver's intention and running environment and apredetermined rule for fuzzy inference, wherein said speed-changecontrol unit changes the gear ratio based on the thirdgear-ratio-change-command generatied by the fuzzy inference means.
 8. Acontrol apparatus for an automatic transmission of a vehicle accordingto claim 7 , wherein the fuzzy inference is performed by weighting thefirst gear-ratio-change-command as compared with the secondgear-ratio-change-command.
 9. A method of controlling an automatictransmission for a vehicle, in which gear change of the automatictransmission is changed based on conditions of speed-change setting thevalues of the target driving torque to vehicle speeds in which a load ofan engine for the vehicle is set as a parameter, comprising the stepsof: changing the conditions of speed-change based on an operation modeselected from at least two modes, a mode which aims at the improvementof acceleration and a mode which aims at the improvement of fuelconsumption rate, correcting a value of a target driving torque by usinga driving torque obtained based on a value indicative of a running stateof the vehicle, a vehicle speed, an engine speed and an turbine speed ofa torque converter for the automatic transmission, wherein the magnitudeof variation of the engine speed to variation of the engine load is setso that the magnitude in a mode which aims at the improvement ofacceleration may be larger than that in a mode which aims at theimprovement of fuel consumption rate at an area of a low load, and themagnitude in a mode which aims at the improvement of fuel consumptionrate may be larger than that in a mode which aims at the improvement ofacceleration at an area of a high load.
 10. A method of controlling anautomatic transmission for a vehicle according to claim 9 , furthercomprising the steps of : inferring a adaptation coefficient based on apredetermined rule for fuzzy inference, and changing the conditions ofspeed-change by using the fuzzy inference for determining the adaptationcoefficient based on the extent of the increase and decrease of theinferred adaptation coefficient.
 11. A method of controlling anautomatic transmission for a vehicle according to claim 9 , wherein theconditions of speed-change is changed by using the fuzzy inference forinferring the extent of the increase and decrease of a adaptationcoefficient and determining the adaptation coefficient based on theextent of the increase and decrease.